Johann Martinez,* Christopher C. Chen, Luca Brillante, and S. Kaan Kurtural *University of California, Davis, Oakville Experiment Station,
1380 Oakville Grade Road, Oakville, CA 94562 (jdmar@ucdavis.edu)

The incidence of solar radiation on red grapes can promote synthesis of phenolic compounds desirable in wine production. However, excess solar radiation may induce oxidative damage and increase berry temperature. Under such conditions, metabolites such as organic acids, flavonols, proanthocyanidins, and anthocyanins may break down, leading to worsened quality. We performed a shade cloth trial to evaluate whether these can mitigate the deleterious effect of overexposure to solar radiation. The experiment was conducted in Oakville, CA, on Cabernet Sauvignon with a relaxed VSP in rows oriented NW to SE. The fruit zone was covered with four polyethylene 1-m curtains (20% shade Pearl, 40% shade Blue, 40% shade Red, 40% shade Black, and 40% shade Aluminet) with different opti-cal properties placed at the fruit zone and a control with no cover. Grape berries were sampled at six developmental stages to determine berry mass, total soluble solids (TSS), pH, total acidity (TA), total flavonols, anthocyanins, and proanthocyanidins. Berry temperature was 3.7°C higher on the west side of the control than on Black. Berry weight under Aluminet was lower than the other treatments. There was a non-significant trend in TSS where Pearl, Aluminet, and control had higher values than Blue and Black. Berries under the cloths had often significantly lower pH and higher TA than control, but only Black showed significant effects at harvest. Berry anthocyanin content tended to be higher under the nets, while flavonol content was significantly higher in the control. Proanthocyanidin content at harvest was higher in Black. Mean degree of polymerization (mDP) of proan-thocyanidins was not affected by treatments. Our results provided evidence that shade cloths may mitigate temperature spikes while transmitting enough radiation into the fruit zone to achieve a better grape composition than uncovered grapes.

Funding Support: HP Olmo Research Funds